December

2007

 * December 11, 2007 - Kaiko, introduction date (assumption based on video upload)
 * December 16, 2007 - Meito, introduction date (assumption based on video upload)

2011

 * December 11, 2011 - Yugata Kichigai is introduced
 * December 17, 2011 - Katsura Ryou is introduced